Add next event estimation

ray-tracing-material/src/lib.rs

@@ -1,4 +1,4 @@
 pub mod default;
 pub mod diffuse;
-
+pub mod microfacet;
 pub mod mirror;

ray-tracing-material/src/microfacet.rs

@@ -0,0 +1,64 @@
+use ray_tracing_core::{material::Material, prelude::*};
+use std::fmt::Debug;
+
+#[derive(Debug)]
+struct Microfacet<D: MicrofacetDistribution + Debug> {
+    dist: D,
+    color: Color,
+}
+
+fn fresnel(w_in: Dir3, n: Dir3, nu_rel: Float) -> Float {
+    todo!()
+}
+
+impl<R: Rng, D: MicrofacetDistribution + Debug + Sync> Material<R> for Microfacet<D> {
+    fn eval(
+        &self,
+        w_in: ray_tracing_core::prelude::Dir3,
+        w_out: ray_tracing_core::prelude::Dir3,
+        _rng: &mut R,
+    ) -> ray_tracing_core::prelude::Color {
+        let w_h = (w_in + w_out).normalize();
+
+        let g = self.dist.g1(w_in, w_h) * self.dist.g1(w_out, w_h);
+
+        self.color * fresnel(w_in, w_h, 1.0) * g * self.dist.d(w_h) / (4.0 * w_in.y() * w_out.y())
+    }
+}
+
+struct BeckmannDistribution {
+    alpha: Float,
+}
+
+impl MicrofacetDistribution for BeckmannDistribution {
+    fn g1(&self, w: Dir3, w_h: Dir3) -> Float {
+        if w.y() > 0.0 && Dir3::dot(w, w_h) > 0.0 {
+            let cos_theta = w.y();
+            let a = self.alpha * (Float::sqrt(1.0 - cos_theta * cos_theta) / cos_theta);
+            (3.535 * a + 2.181 * a * a) / (1.0 + 2.276 * a + 2.577 * a * a)
+        } else {
+            1.0
+        }
+    }
+
+    fn d(&self, w_h: Dir3) -> Float {
+        if w_h.y() > 0.0 {
+            let cos_theta_squared = w_h.y() * w_h.y();
+            1.0 / (FloatConsts::PI
+                * self.alpha
+                * self.alpha
+                * cos_theta_squared
+                * cos_theta_squared)
+        } else {
+            0.0
+        }
+    }
+}
+
+trait MicrofacetDistribution {
+    fn g1(&self, w: Dir3, w_h: Dir3) -> Float;
+
+    fn d(&self, w_h: Dir3) -> Float;
+
+    // fn sample_d(&self) -> Dir3;
+}